Rhamphostomella alutacea Gontar, 1993

Grischenko, Andrei V., Gordon, Dennis P., Taylor, Paul D., Kuklinski, Piotr, Denisenko, Nina V., Spencer-Jones, Mary E. & Ostrovsky, Andrew N., 2022, Taxonomy, ecology and zoogeography of the Recent species of Rhamphostomella Lorenz, 1886 and Mixtoscutella n. gen. (Bryozoa, Cheilostomata), Zootaxa 5131 (1), pp. 1-115 : 37-40

Rhamphostomella alutacea Gontar, 1993

( Figs 10 , 32C–E )

Rhamphostomella alutacea Gontar, 1993a, p. 12 , fig. 7.

Rhamphostomella alutacea: Denisenko 2013, p. 184 .

Material examined. Holotype: ZIRAS 1 /44569, colony encrusting skeleton of sea urchin, Kuril-Sakhalin Expedition of Zoological Institute ( ZIRAS) and Pacific Institute of Fisheries and Oceanography ( TINRO), 15 September 1949, Krabovaya Bight, Shikotan Island, Lesser Kuril Ridge, Pacific Ocean, depth 55 m, shell, rock dredge, collector E.F. Guryanova. Paratype: ZIRAS 2 /50123, five fragments of single colony detached from broken shell of the bivalve Chlamys sp ., MFRT Rodino, 12 September 1992, about 32 km from Cape Hayryuzova, western Kamchatka shelf, Sea of Okhotsk , 57°36.2ʹ N, 156°09.0ʹ E, depth 78–81 m, crab trap, collector A . V. Grischenko .

Measurements. ZIRAS 2/50123, western Kamchatka, Sea of Okhotsk ( Fig. 10A–L ). ZL, 0.60–0.93 (0.71 ± 0.09). ZW, 0.35–0.55 (0.44 ± 0.05). ZD, 0.59–0.65 (n = 2). OrL, 0.15–0.25 (0.19 ± 0.03). OrW, 0.20–0.27 (0.22 ± 0.02). OeL, 0.17–0.27 (0.24 ± 0.03). OeW, 0.24–0.35 (0.30 ± 0.03). Av(s)L, 0.07–0.14 (0.10 ± 0.01). P(m)N, 16–26 (19). P(oe)N, 1–10 (6).

Description. Colonies encrusting, multiserial, unilaminar ( Fig. 10A ), irregular in form, attaining 33 mm in maximal dimension; bright red to orange when alive, dark red to pink when dry. Zooids of medium size, hexagonal, oval to pyriform or irregular, arranged in quincunx, demarcated by fine, meandering sutures between lateral and transverse walls ( Fig. 10A, D–H ); boundaries less distinct in older parts of colony.

Frontal shield umbonuloid ( Fig. 10A, D, I ), thickened, pustulose, convex in young zooids, flattened and smoother in older ones owing to its thickening. Large, deep, round to oval areolae along margins ( Fig. 10D–H ), separated by short narrow interareolar ridges that may reach suboral avicularian cystid in distal part of frontal shield, mainly in young zooids. Thickening of frontal shield in older parts of colony resulting in considerable change in appearance, with some areolae reduced in size and obliterated, and others partitioned, resulting in “migration” of openings toward central part of shield and possibly fusing (compare Fig. 10A, D, E with Fig. 10F–H ). Umbonuloid component extensive, occupying about 60% of length of frontal shield (63% in one measured zooid). Ring scar discrete ( Fig. 10I, K ), forming regular boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure.

Primary orifice ( Fig. 10A, B ) submerged, broadly circular or oval; distal and lateral margins formed by upper terminal part of distal transverse wall, with ill-defined rim ( Fig. 10A, B, D, E ). Distal margin of orifice rounded; proximal margin concave, with elongate to short, blunt or bifurcate median lyrula and two small acute or blunt processes situated proximolaterally. Sometimes one or both processes strongly reduced or absent ( Fig. 10A, D–F ). No condyles or oral spines.

Secondary orifice ( Fig. 10E–H ) round to oval, cormidial, formed distally by slightly elevated vertical walls of distal zooid and occasionally by lateral walls of neighbouring zooids ( Fig. 10D, E, G ); proximally restricted by thin walls of peristome, comprising two relatively tall, symmetrical lappets derived from frontal shield and incorporating avicularian cystid medially; lappets connecting to proximolateral corners of ooecium in ovicellate zooids ( Fig. 10F, H ).

Cystid of suboral avicularium small, occupying less than one-quarter of zooid frontal shield; low in young zooids ( Fig. 10A, D, E ), moderately to strongly elevated and conical in some older zooids; situated medially or (more often) lying transversely to left or right of median axis. Frontal surface (rostral/postmandibular areas) crossing zooidal midline. Rostral frontal surface at strong oblique angle to postmandibular area, overall facing laterally and obliquely frontally; this concave aspect of avicularium, as well as position in peristome, gives impression of pseudosinus in secondary orifice. Rostrum short, blunt, semioval, directed laterally to distolaterally and upwards ( Fig. 10C ); palatal foramen conforming to shape of rostrum, no cryptocystal shelf; opesia semicircular or lingulate, sometimes of same size as foramen. Crossbar complete.

No adventitious avicularia.

Ovicells initially hyperstomial, rapidly becoming subimmersed and even appearing endozooidal ( Fig. 10F–H, L ) through overgrowth by secondary calcification from adjoining daughter and neighbouring zooids that cover most of ooecium except for central pseudoporous part. Ooecium formed by distal autozooid. Ooecial and visceral coelomic cavities connected via communication canal opening on underside of frontal shield of distal zooid as large, angular communication slit near proximalmost areolae ( Fig. 10I ). Ooecium with straight or slightly concave proximal margin. Ectooecium smooth, with pseudopores varying markedly in number, size, form (round, oval, elongate, irregular) and pattern of arrangement.

Zooids interconnected by one mural pore chamber in each distolateral wall ( Fig. 10L ). Predominantly two (occasionally one) multiporous septula sometimes added by individual pores in basal half of transverse walls. In some zooids, transverse wall has two shallow recesses separated by medial buttress.

Basal surface of zooids ( Fig. 10J ) fully calcified, convex, smooth or with coarse transverse lineation; without evident protuberances. Boundaries between zooids recognizable basally by deep, sinuous incisions.

Ancestrula and early astogeny not observed.

Remarks. Rhamphostomella alutacea differs from congeners in the strictly transverse position of the suboral avicularium, which is strongly angled upon itself to appear concave, with the rostrum facing obliquely frontally. The only congener with a similar transverse placement of the suboral avicularium, R. radiatula , has a narrow, U-shaped pseudosinus, with the avicularian rostrum often hidden or barely visible frontally ( Fig. 18D–H ).

In her original description, Gontar (1993a) mentioned and illustrated ovicells as having an ooecium with a single triangular or slit-like central pseudopore. In fact, the number, shape, and arrangement of the pseudopores can vary markedly ( Fig. 10F – H ). Contrary to the original description of the frontal shield as flattened, we observed that it can be convex in young zooids.

Ecology. Rhamphostomella alutacea was recorded from 55–81 m depth on sandy and silty bottoms overlain with gravel, where colonies encrust broken shells of the bivalve Chlamys sp. and sea urchin tests.

Distribution. This species was originally described from Krabovaya Bight, Shikotan Island, Lesser Kuril Ridge, northwestern Pacific; we report it also from the western Kamchatka shelf, Sea of Okhotsk. Thus, R. alutacea is a Pacific Asian boreal, sublittoral species.

Figures

FIGURE 10. Rhamphostomella alutacea Gontar, 1993. ZIRAS 2/50123 (western Kamchatka, Sea of Okhotsk). A. Colony margin with developing zooids. B. Orifice, showing median lyrula and lateral denticles. C. Close-up of suboral avicularium. D, E. Group of non-ovicellate zooids in young part of colony. F, G. Ovicellate zooids in older part of colony, with ooecia embedded in secondary calcification arising from surrounding zooids. H. Close-up of ovicellate zooid, with coarsely granulate frontal shield and ooecium having pseudopores overlain with secondary calcification. I. Interior of the frontal shield, showing ring scar, areolae and proximal area with chevron-shaped communication slit of ooecium (arrow). J. Basal colony surface. K. Close-up of frontal shield interior, showing ring scar and exterior wall microstructure of umbonuloid component. L. Lateral view of zooidal lateral wall, showing mural pore chambers, and ooecium (to the right) embedded in secondary calcification. Scale bars:A, J, 500 μm; B, H, I, 100 μm; C, K, 50 μm; D–G, 250 μm; L, 200 μm.

FIGURE 18. Rhamphostomella radiatula (Hincks, 1877).ZIRAS 19/50114 (Medny Island, Commander Islands, Bering Sea).A. Developing zooids with forming ooecia near colony margin. B. Distal view of marginal zooids with developing ooecia (arrows). C. Suboral avicularium. D. Non-ovicellate zooids in relatively young part of colony.E.Ovicellate (to the right) and non-ovicellate zooids with well-developed, bulge-like coarse tubercles of secondary calcification in older part of colony. F. Single ovicellate zooid, showing form of secondary orifice and ooecium in relatively young part of colony. G. Group of ovicellate zooids with ooecia overgrown by secondary calcification in relatively young part of colony. H. Distal view of ovicellate zooids, showing suboral avicularium and median process in older part of colony. I. Interior of frontal shield, showing lyrula, ring scar and areolae. J. Close-up of frontal-shield interior, showing median lyrula. K. Basal surface of colony that was overgrowing another bryozoan colony, Celleporella hyalina. L. Interior of frontal shield, showing ring scar and exterior wall microstructure of umbonuloid component. M. Lateral section of zooids showing two ooecia, suboral avicularium, areolae (upper row) and zooidal lateral walls with mural pore chambers. Scale bars: A, B, G, H, 250 μm; C, J, L, 50 μm; D, K, 500 μm; E, F, I, 100 μm; M, 200 μm.

FIGURE 32. Type specimens of Rhamphostomella species. A, B. Rhamphostomella gigantea Osburn, 1952. Holotype, USNM 11033 (Point Barrow, Alaska, Beaufort Sea). C–E. Rhamphostomella alutacea Gontar, 1993. Holotype, ZIRAS 1/44569 (Krabovaya Bight, Shikotan Island, Lesser Kuril Ridge, Pacific Ocean). F, G. Rhamphostomella bilaminata (Hincks, 1877). Neotype, NHMUK 1911.10.1.1580A (Gaspe, Gulf of St Lawrence, Atlantic Ocean). H, I. Rhamphostomella hincksi Nordgaard, 1906. Neotype, NHMUK 1976.8.6.39pt (about 22 km westwards from Medvezhii Island, western Barents Sea). J, K. Rhamphostomella plicata (Smitt, 1868). Lectotype, SMNH-Type-1696 (Waygat Islands, Hinlopen Strait, Svalbard and Jan Mayen). L, M. Rhamphostomella radiatula (Hincks, 1877). Neotype, NHMUK 1911.10.1.1592 (Iceland). Scale bars: A, B, D–G, K, M, 250 µm; C, H, I, J, L, 500 µm.